There is a desire to produce air-drying stains with a high content of nonvolatile matter and a low content of volatile solvents. These stains and finishing coats for wood are to be processed (painted, brushed) by laymen as well as by experts. Chemically modified natural oils are used to produce such stains with high contents of nonvolatile mater. On the other hand, there are also other stains, which are mixed solely on the basis of water. The stains based on natural oils penetrate deeply into a wood substrate. The finish does not swell the wood, which is protected against embrittlement and drying out. Since only one coat needs to be applied, application possibilities arise for saving time and materials.
However, when applying known air-drying stains, it has turned out in isolated cases that the painted wood surface, when dry, develops a "spotty" or mottled appearance. This appearance, which reduces the value of the surface, arises because of incomplete penetration of the stain with its nonvolatile matter into the wood. It is as if islands of high concentrations of solids remain behind at the surface and cause the finish to appear to be inhomogeneous.